This invention relates to the field of abrasives and, more particularly, to synthetic diamond grit, abrasive media produced using synthetic diamond grit, and methods and apparatus for making synthetic diamond grit and other superabrasive grit.
The use of natural diamond grit for applications such as polishing and for cutting and grinding wheels is very old. In addition to the limitations of high cost, natural diamond grit cannot be readily provided with characteristics that are "tailored" for particular abrasive applications. Also, for some abrasive uses, a limitation of natural diamond is the difficulty of obtaining the grit in an elongated or high aspect ratio configuration that is advantageous for certain applications.
Experiments aimed at creation of synthetic or artificial diamond from carbonaceous material were performed as early as the nineteenth century. It was not until the 1950's, however, that successful synthesis of diamond was achieved. The synthesis technique was a so-called high-pressure high-temperature ("HP-HT") method wherein diamond is produced by highly compressing carbon, in the form of graphite, at high temperature in the presence of a catalyst. HP-HT techniques are currently used to synthesize diamond for various uses, and HP-HT diamond is presently the dominant source of diamond grit for abrasive media.
HP-HT diamond can be produced with characteristics tailored, to some extent, for particular abrasive grit applications; for example, by selecting synthesis conditions to obtain desired morphology, shape and/or defect distribution that will result in a desirable friability for a particular grinding application. However, HP-HT processes generally use a metallic catalyst such as nickel, iron or cobalt, and the resultant HP-HT diamond may contain substantial metallic inclusions that can introduce undesirable operating properties in abrasive media made with HP-HT diamond. For instance, the inclusion of cobalt leads to conversion of the diamond material to graphite at elevated temperatures, which may be encountered near the cutting edge of diamond film cutting tools.
It is among the objects of the present invention to provide a method of making diamond grit that is substantially free of metal inclusions and which has properties that can be tailored toward particular abrasive media applications. It is also among the objects of the present invention to provide an apparatus for making diamond grit and other superabrasive grit.